Ion beams are often scanned across a target within an evacuated treatment chamber using electrostatic or electromagnetic means. Electrostatic scanning has the disadvantage that at high ion beam currents the ion beam blows up under internal space charge forces. Magnetic scanning involves the use of large magnets, it is often clumsy, expensive, and increases the beam line length, and thus requires a long chamber. These problems are accentuated when it is desired to treat large target areas with high ion beam currents. Use of mechanical motion to sweep an ion beam by configuring the ion source and extraction electrode as an ion gun faces a number of difficulties because the apparatus should be simple, compact, and avoid large seals, the relationship between the ion source and the extraction electrode must be held to close tolerance and the ion accelerating voltage, often in the range of 50 to 120 kilovolts or higher, must be held between the ion source and the adjacent extraction electrode. Insulation between these closely positioned parts is difficult in the hostile vacuum environment of high voltages, high ionization and the presence of un-ionized gas molecules that escape from the ion source.
Similar problems are faced with other scanning devices in treatment chambers which employ high voltages or other conditions.